Ministers must provide “urgent clarity” on the UK’s post-Brexit immigration system to avoid placing “unrealistic expectations” on already-stretched staff, the FDA has warned MPs.

Appearing before the Home Affairs Select Committee in November, FDA National Officer Helen Kenny – who represents senior staff in the Home Office – highlighted significant pressures in a department which has cut its headcount by more than 1,000 since 2010.

Pointing to the FDA’s latest working hours survey, carried out earlier in 2017, Kenny said almost three-quarters of the union’s Home Office members believed working excessive hours is already a problem in their organisation.

She added: “Over 60% say that they’ve worked while on sick or annual leave, and most feel that that’s not going to change, that nothing is being done about the workload. So the issue isn’t necessarily vacancies. It’s – having cut the workforce – the amount of additional pressure on people who have remained.”

A key issue facing Home Office staff in the months ahead will be the registration of the three million EU nationals currently in Britain, Kenny said. But while work on the registration system was already well underway, she said it could not be finalised until the outcome of Brexit negotiations is clear.

Kenny told the Committee that there was a “frustration” among FDA members in the Home Office at the length of time taken to fill vacancies, and warned that their “biggest concern” is “not knowing what things will look like the day after we leave the European Union”.

“The closer we get to that date the more likely it is that Home Office will not have the time or the resources or the ability to put the relevant processes in place,” she added. “There’s a real concern that the Government will expect the impossible. That unrealistic expectation of how quickly a system can be put in place is causing real concern for our members.”